The long range goal of this research program is to understand structure/function relationships that underlie the processing of information into, through, and out of visual cortex. Experiments proposed here address questions about the afferent input to areas 17 and 18 that arises from the lateral geniculate nucleus (LGN) in the cat. The impetus for the experiments is my recent anatomical finding that the sublaminar of single X- and Y-cell axons in layer IV of area 17 are strongly related to retinal cells' soma positions within the depths of the geniculate A-laminae (i.e., lamina A and Al). The present goal is to understand the functional significance of this positional and projectional relationship, both within the LGN and within area 17, and to determine whether analogous relationships hold in the geniculocortical projections to area 18. Specific aims are as follows: (1) To determine for X- and Y-cells what relationship exists between a cell's position within the depth of its A-lamina and its functional properties. Methods used will be extracellular recording and quantitative analysis of visual response properties (viz., spatial and temporal frequency tuning, peak contrast sensitivity, latency and discharge pattern to visual stimulation). Similar tests will be used to characterize Y-cells in lamina C and the medial interlaminar nucleus (MIN). (2) To determine whether differences in the sublaminar projections of X- and Y-cell axons in layer IV and VI of area 17 reflect differences in the cell's visual response properties. Single geniculocortical axons will be recorded in visual cortex, their visual resonse properties will be identified, and they will be labeled by intracellular injections of horseradish peroxidase to visualize their axon terminal arbors in cortex and their cell bodies in the LGN. The sublaminar projections of Y-cell axons in area 18 will also be examined. (3) To determine whether the visual response properties of Y-cells projecting to area 18 differ from those of Y-cells projecting to area 17. (4) To determine the sublaminar projections of W-cell axons arising from the parvocellular C-laminae of the LGN. The results obtained will reveal basic rules of organization in the geniculocortical projections in the cat, and lead to a better understanding of the type of visual information which is distributed to cortical cells in different sublaminae within areas 17 and 18.